1. (Field of the Invention)
This invention relates to an evaluation method of corrosion of a steel material embedded in a concrete which evaluates the corrosion state of the steel material in a reinforced concrete (RC) structure on the basis of three parameters, i.e., corrosion potential measured by one or more reference electrodes locatable or disposed on the concrete surface, the actually measured values of polarization resistance and concrete resistance (liquid resistance) that are measured by applying currents between one or more sensors locatable or disposed on the concrete surface and the steel material, and more particularly to an evaluation method of corrosion of a steel material inside a concrete which makes it possible to make absolute evaluation of the corrosion state and to improve the evaluation accuracy.
2. (Prior Art)
The problem of corrosion of a steel material in concrete is one of the most critical problems relating to durability of a concrete structure and various researches have so far been made for establishing evaluation methods of the corrosion state. Among them, non-destructive evaluation methods of corrosion state include a method which measures corrosion potential (in accordance with the ASTM standards) on the concrete surface, a method which judges the occurrence of corrosion from the result of observation with eyes, a method which measures the polarization resistance by applying currents between electrodes disposed on the concrete surface and the steel material inside the concrete, and diagnoses corrosion on the basis of the measurement results, and a method which measures corrosion potential and concrete resistance together with the polarization resistance, and examines collectively the corrosion state on the basis of these results (Japanese Patent Laid-Open No. 217147/1984). Furthermore, there is a method which conducts a neutralization test and a method which judges the corrosion state by measuring the decrease in diameter of a steel bar by a pacometer.
Destructive methods which involve destruction of the concrete includes a method which chips the concrete cover and observes the sample with eyes, a method which measures salt concentration, and the like.
However, the method described above which measures the corrosion potential, the polarization resistance or the concrete resistance handles merely the measurement values themselves and involves the problem that relative comparison can be made only under the same boundary condition, the method cannot make absolute evaluation. Since these objects being measured change with the boundary condition or with a temperature, it involves another problem that its evaluation accuracy is low.
On the other hand, the method which relies on the mere observation with the eyes involves the problem that evaluation can be made only after corrosion has considerably proceeded to some extent as to provide a rusty solution and rusty cracks on the surface of the concrete. The neutralization test method cannot recognize the corrosion in the case of progress of corrosion by salts and the test itself becomes meaningless. In the case of the method which measures the diameter of the reinforcing steel by the pacometer, no pacometer capable of measuring the diameter with accuracy of below 0.1 mm is available at present, and this method cannot detect corrosion of the reinforcing steel inside the concrete wherein cracks in the axial direction are believed to occur by the reduction of thickness of below 0.1 mm.
Furthermore, the method by salt concentration measurement and the direct and high accurate method involving chipping have the drawback that they involve destruction. The salt concentration measurement method is after all environmental evaluation and does not directly relate to corrosion evaluation of the reinforcing steel.
In view of these problems with the prior art methods, this invention contemplates to provide an evaluation method of steel material corrosion which can make quantitative, highly accurate and more detailed evaluation of not only the corrosion state at the present but also the corrosion progress in the future without being affected by the environmental condition.